The treatment of back pains still remains a challenge for many reasons. One of such reasons is the difficulty to permanently and exclusively cure the cause of such pains without affecting surrounding tissues in an area of a human body that is a main channel of nerve impulse.
Different causes of back pain exist. Of all chronic low back pain problems, about 20% can be attributed to the facet joints. This cause is also known as the chronic lumbar facet joint syndrome. Among patients, 90% are successfully treated through conservative procedures such as active physiotherapy and NSAIDS. For the remaining 10%, further investigation as well as a more aggressive therapeutic approach must be considered. Once the diagnosis of the facet joint syndrome is clinically made, percutaneous thermotherapy procedures may be considered, seeking a minimally invasive treatment with low morbidity and satisfactory clinical efficiency.
Discogenic back pain, another cause of back pain, is responsible for close to 60% of chronic low back pain in the general population. Once conservative treatment has been fully used, 5% of the patients remain with back pain that can be considerably invalidating. Usual treatment of this invalidating condition is spinal fusion or disc arthroplasty, both associated with considerable morbidity, off-work time, and social cost. Clinically discogenic pain patients have constant back pain that is amplified in the vertical disc loading positions, with a sitting being even worse or equal to the standing position pain. Disc pain is reproduced by pain provocation procedures such as discograms or discometry. Denervation of a portion of the disc, to relieve some if not most of the pain by a percutaneous procedure, is a known advantageous alternative with a reduction of the cited disadvantages of the more aggressive procedures.
Cryotherapy exists as therapy of discogenic back pain or facet joint syndrome since 1961. However, this technique originally used liquid nitrogen as coolant, reaching a treatment temperature of approximately −80 C.°., while the trocar was placed under fluoroscopic guidance. Limited control of the cryoanalgesia process with this combination of technology has resulted in only temporarily pain relief. Studies even showed that there does not exist statistical differences between patients who had such a treatment and patients treated with a placebo pr probe. On the other hand, a study showed that irreversible damage to the nervous structures is obtained only when temperatures reach below −140 C.°. Temperatures above −140 C.° only temporarily affect the nerve tissue.
It is therefore possible to divide thermotherapy in two types: moderate and extreme temperature thermotherapy. Moderate temperature thermotherapy only temporarily affects nerve tissues and therefore does not cause permanent damages. Consequently, pain relief is only temporary. Monitoring of such treatments is not as critical as it is with extreme temperature thermotherapy. Should the probe affect tissues that should not have been affected, the effects would only be temporary. Extreme temperature thermotherapy (either extremely high or extremely low temperatures), on the other hand, causes permanent damages to tissues. Destroying tissue with this type of treatment is desirable in order to permanently remove pain generators in a body by destroying the nerves in tissues of any nature, or to treat tumors of any kind in a minimally invasive fashion, such as percutaneously. Because of its permanent effects on the body, careful monitoring of the effects of a probe used for extreme temperature treatment is mandatory. Furthermore, cold, whose propagation is far more predictable in the human body than heat, is more often used for extreme temperature treatment. It follows that careful monitoring of a growth of an ice ball of treated tissues created by a cryoprobe is necessary, especially when treating chronic lumbar facet joint syndrome, where inadequate propagation of the ice ball could affect spinal tissues and permanently paralyze a patient. Up to now, monitoring the size of the ice ball was realized either by imagery or by temperature monitoring. Temperature monitoring is accomplished by positioning a temperature sensor that will detect a variation in a temperature of the surrounding tissues and, consequently, the presence of the ice ball. Doing so requires separately inserting in the patient's body the cryoprobe and at least one temperature sensor. Then, X-ray, or another imaging method, must be used to verify a position of the temperature sensor with respect to the cryoprobe.
Imagery monitoring typically uses technologies such as MRI, CT scanning, or ultrasound. However, simultaneously using such imagery systems while operating adds to the complexity of the operation.
Different types of cryoprobes have been suggested. For example, U.S. Pat. No. 6,551,309 describes a cryoprobe comprising, at its tip, several sensors used to monitor that the tip is cooled. However, these sensors are laid out on a thermally and electrically conductive surface and are therefore only adapted to measure the temperature of the tip of the cryoprobe but not that of the surrounding tissues. Consequently, this cryosurgery system requires the use of an MRI imaging system.
US patent application No. 20040024391 describes an apparatus and a method to protect certain tissues during a cryosurgery. This document describes a probe provided with a temperature sensor laid out on a portion remote from its tip. The temperature sensor is used to follow a change of the induced temperature to treated tissues. However, this document does not disclose placing the temperature sensor at a specific distance from the tip such as to monitor the growth of an ice ball and control the cooling by the probe accordingly. Consequently, the apparatus and method described in this document still requires the use of an imagery method such as X rays, ultrasounds, CT or MRI.
There is therefore a need for an improved system for percutaneous thermotherapy that does not require constant visual monitoring of the surgery so that such treatment may be conducted without resorting to imagery systems, which may not be available in all health facilities, and that does not require the use of an additional external temperature sensor.